[accordion] inconsistent behaviour in accordionchange

Description

Pretext: accordion configured with "active" set to false, and "alwaysOpen" set to false.

There's an inconsistency in the behaviour of the "oldContent" and "newContent" properties that are passed as data to the accordionchange event handler.

When opening any item while the entire accordion is collapsed, the "oldContent" will contain 0 elements as expected. However, when closing all open items, the "newContent" will contain the last opened item, which seems inconsistent as all items are closed and there is no content to be displayed.

One would expect that when closing the only open item, "oldContent" contains the last opened item, and "newContent" is set to empty.